To prevent tooth decay, the advantages of regular brushing have long been recognized. The optimal brushing technique is to move the toothbrush bristles in small orbital movements. This may be accomplished using manual toothbrushes having the toothbrush head and bristles thereon fixed to the neck of the brush, by the brusher moving his hand in small circles.
To provide a large number of brush strokes in small time periods, electric toothbrushes are often used. These are configured somewhat differently however, usually having a circular bristle array that rotates about its axis. Such a brushing motion is inherently inferior to the small orbital brush strokes of the manual operated toothbrush, and the brush head is typically rather smaller than that of manual toothbrushes, resulting in only one or two teeth being brushed at one time. However the larger number of brush strokes obtainable by electrical toothbrushes goes a long way to overcome this disadvantage.
Recent developments in manual toothbrushes combine different bristle types. For example, one combination has outer layers of soft bristles or rubber spikes to massage gums and inner layers of hard nylon bristles for scraping enamel surfaces of teeth, to remove plaque and scale. It will be appreciated, that such combinations are not obtainable on rotating circular brush heads, and thus are not provided by electrical toothbrushes.
There have been several attempts to obtain the effect of manual brushing with electrical toothbrushes, and there are several hundred electrical toothbrushes in the prior art. Some have two drive systems to move the brush head back and forth in two direction pairs, substantially perpendicular to each other and to the bristles themselves. Such motorized toothbrushes either brush in both direction pairs simultaneously but at different frequencies, or can be operated to brush in one direction pair, such as from side to side with respect to the toothbrush handle, and then in the other direction pair, such as inwards and outwards with respect to the toothbrush handle. Some prior art toothbrushes use piezoelectric chips to drive the toothbrush head back and forth ultrasonically. Most use simple rack and pinion gears.
Combination toothbrushes with fixed bristle arrays and rotating bristle array are also known. These go some way to providing the advantages of both electrical and manual brushing in a single toothbrush. However, in general, electrical toothbrushes have not superseded manual toothbrushes because none provide the effects of the preferred circular strokes of correct manual brushing in a reliable manner.
U.S. Pat. No. 4,791,945 to Moriyama describes a power operated toothbrush including a brush supporting arm which is pivoted on two crank means. The distance between a crank shaft and a crank pin of one of the crank means is continuously changed so that the turning motion or oscillatory motion of a brush member which is mounted on an end of the brush supporting arm can be produced and one of the motions can be continuously changed to the other. One embodiment described therein is a power operated toothbrush including a hollow casing, an electric motor within the casing, means for energizing the electric motor, a pair of cranks spaced apart longitudinally of the hollow casing having eccentric drive pins thereon, means for rotating the cranks the same amount and at the same speed from the electric motor including bevelled gears secured to the motor and to one of the cranks, a spur gear on each of the cranks and a series of spur gears connecting the cranks to each other for simultaneous similar rotation, a toothbrush member having bristles on one end thereof, means for securing the other end of the toothbrush member to one of the cranks and means for securing the other of the cranks to the toothbrush member centrally thereof and means operably associated with at least one of the cranks for varying the eccenticity of the eccentric pin thereon to vary the motion of the bristles of the toothbrush between a complete circular orbital motion and a reciprocal arcuate motion. The toothbrush described therein can be set to achieve the desired orbital brushing, since the neck of the toothbrush can be set to reciprocate in an elliptical manner with regards to the handle. However, since the large neck and head move backwards and forwards, a large motor is required and the power drain on the batteries is considerable. Such toothbrushes are impractical, expensive to manufacture and liable to failure, not least because of the difficulty of sealing the handle against moisture penetration.
Ideally, therefore, a mechanical toothbrush having a head with a rectangular array of bristles thereon, is required, such that the rectangular array of bristles is driven by a mechanism in an orbital path simulating the movement imparted to the toothbrush head and bristle array of a manual toothbrushes operated in a correct brushing manner by the user, and the present invention provides such a mechanical toothbrush.